Silver Lake Reservoir Complex Storage Replacement Project SCH #

Transcription

1 Addendum to the Final Environmental Impact Report Silver Lake Reservoir Complex Storage Replacement Project SCH # Los Angeles Department of Water and Power Environmental Affairs 111 North Hope Street, Room 1044 Los Angeles, California December 2013

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3 Silver Lake Reservoir Complex Storage Replacement Project Table of Contents Section 1 Section 2 Introduction 1.1 Purpose of the Addendum Project Overview Approved Bypass Pipeline Alignment Reconsideration of In-Reservoir Pipeline Alignment Environmental Impact Assessment 2.1 Land Use Earth Resources Water Resources Biological Resources Cultural Resources Paleontological Resources Traffic and Transportation Noise Air Quality Public Services and Utilities Hazardous Materials Visual Resources Other Environmental Issues List of Figures Figure 1 Approved Bypass Pipeline Alignment... 4 Figure 2 Refined Bypass Pipeline Tunneling Alignment... 7 Figure 3 Redesdale North Tunneling Shaft Figure 4 Redesdale South Tunneling Shaft Figure 5 Putnam Tunneling Shaft Figure 6 In-Reservoir Pipeline Alignment Figure 7 Work Areas 1 and Figure 8 Work Area List of Tables Table 1 Bypass Pipeline Tunneling Alignment Construction Activities Table 2 In-Reservoir Pipeline Alignment Construction Activities December 2013 Page i

4 Table of Contents Acronyms and Abbreviations CEQA DB DBA EIR EPBM LADWP L eq MG NO x O 3 PM 2.5 PM 10 PSI SCAQMD SLRC California Environmental Quality Act decibel a-weighted decibel Environmental Impact Report earth pressure balance machine Los Angeles Department of Water and Power community equivalent noise level million gallons nitrogen oxides ozone particulate matter less than 2.5 microns in diameter particulate matter less than 10 microns in diameter pounds per square inch South Coast Air Quality Management District Silver Lake Reservoir Complex Page ii

5 Silver Lake Reservoir Complex Storage Replacement Project SECTION 1 INTRODUCTION 1.1 Purpose of the Addendum This addendum to the previously certified Environmental Impact Report (EIR) for the Los Angeles Department of Water and Power (LADWP) Silver Lake Reservoir Complex Storage Replacement Project (SCH # ) has been prepared in accordance with California Environmental Quality Act (CEQA) Guidelines Section to revise the certified EIR to accurately reflect the changes or additions to the project, changes in conditions under which the project is undertaken, or to add new information. In accordance with CEQA Guidelines Section 15162, changes to the approved project addressed in this addendum would not result in new significant environmental effects or a substantial increase in the severity of previously identified significant effects, as discussed herein. The Final EIR for the Silver Lake Reservoir Complex Storage Replacement Project was certified by the City of Los Angeles Board of Water and Power Commissioners on May 16, 2006, concurrent with approval of the project (Certified EIR). A Notice of Determination for the project approval was filed with the State Clearinghouse and the Los Angeles County Clerk s office on May 18, The approved project in the Certified EIR will remove Silver Lake and Ivanhoe Reservoirs from the LADWP potable water distribution system and relocate the water storage function provided by the Silver Lake Reservoir Complex (SLRC) to the former Headworks Spreading Grounds site, where a new 110-million gallon (MG) buried storage reservoir is currently under construction. The Certified EIR found the proposed project to have significant but mitigable environmental impacts to Earth Resources (Chapter 4), Water Resources (Chapter 5), Biological Resources (Chapter 6), Cultural Resources (Chapter 7), and Paleontologic Resources (Chapter 8). Impacts to Traffic and Transportation (Chapter 9), Noise (Chapter 10), and Air Quality (Chapter 11) would be significant and unavoidable even after incorporation of feasible mitigation measures. A Statement of Overriding Considerations was adopted for these unavoidable impacts. Less than significant impacts to Land Use (Chapter 3), Public Services and Utilities (Chapter 12), Hazardous Materials (Chapter 13), and Visual Resources (Chapter 14) were identified in the Certified EIR. Since the initial project approval, the engineering design for the project has proceeded, establishing a more refined concept for the physical and procedural aspects of project construction than was available at the time of the preparation and consideration of the Certified EIR. Further, it has been determined that a different alignment for an interconnecting pipeline between the River Supply Conduit and the Silver Lake Outlet Line, a component of the project as described and analyzed in the Certified EIR, can be feasibly implemented that would reduce the duration of construction within public roadways and the associated community disruption. Instead of constructing a tunnel beneath West Silver Lake Drive adjacent to the SLRC, the interconnecting pipeline would be located primarily within the SLRC, including within Silver Lake Reservoir, as explained in detail below. In deciding whether a subsequent or supplemental EIR is necessary or if an addendum is appropriate, the standard of review is whether the record as a whole contains substantial evidence to support a determination that the changes in the project or its circumstances are substantial enough to make major modifications to the EIR due to the involvement of new significant environmental effects or a substantial increase in the severity of previously identified significant effects. December 2013 Page 1

6 Introduction The SLRC in-reservoir pipeline alignment has not altered the fundamental objectives of the project as reflected in the Certified EIR. The project would still relocate the SLRC water storage to the Headworks Spreading Grounds site. Long-term project operations are not anticipated to change from what was considered in the Certified EIR. However, based on additional site investigations and more extensive design development, it has been determined that implementation of the interconnecting pipeline would result in changes to the construction phase of activities within and adjacent to the SLRC. In accordance with CEQA, the nature and extent of these changes must be considered in the context of the Certified EIR conclusions regarding project-related environmental impacts to determine if they might create new significant impacts that were not identified in the Certified EIR or substantial increases in the severity of significant impacts that were identified in the Certified EIR. LADWP has developed the in-reservoir alignment for the interconnecting pipeline to minimize community disruption and the associated impacts by reducing the extent and duration of construction within public roadways. As discussed herein, the proposed modifications to the project design would not result in new environmental impacts or increase the severity of previously identified environmental impacts. The following sections provide additional detail regarding the proposed modifications and findings. 1.2 Project Overview As a component of the Silver Lake Reservoir Complex Storage Replacement Project, the reservoir complex will be removed from service as a treated drinking water storage facility, but both Silver Lake and Ivanhoe Reservoirs will continue to be filled with non-potable water. The drinking water storage function of the reservoir complex will be replaced by a new reservoir at the Headworks Spreading Grounds site in Griffith Park. However, because it will not contain potable water, the SLRC will no longer provide a physical link, as it currently does, between the River Supply Conduit (a trunk line that currently supplies drinking water to the SLRC at the north end of Ivanhoe Reservoir) and the Silver Lake Outlet Line (a trunk line that currently supplies water from the SLRC to large areas of the City of Los Angeles south of Silver Lake). Therefore, as described in the Certified EIR, it is necessary to construct a new potable water pipeline to provide a connection between the terminus of the River Supply Conduit and the start of the Silver Lake Outlet Line, which are separated by approximately 1 mile. The recently reconstructed River Supply Conduit terminates north of Ivanhoe Reservoir near the intersection of West Silver Lake Drive and Armstrong Avenue. The Silver Lake Outlet Line commences south of Silver Lake Reservoir, where West Silver Lake Drive turns from eastbound to southbound near the Silver Lake Recreation Center. 1.3 Approved Bypass Pipeline Tunneling Alignment Background As described in the Certified EIR, the interconnecting pipeline would follow an alignment that physically bypasses both Ivanhoe and Silver Lake Reservoirs, rather than an alignment that would route the line through the SLRC. This bypass alignment was chosen primarily because at the time the EIR was certified in 2006, both Silver Lake and Ivanhoe Reservoirs were still active treated drinking water storage facilities providing service to a large area of the City. This was at a time when several of the largest uncovered drinking water reservoirs, including Upper and Lower Hollywood, Encino, and Lower Stone Canyon Reservoirs, had recently been permanently removed from service in order to comply with the conditions of the 1989 Surface Water Treatment Rule. The removal of these four reservoirs from service eliminated approximately 8 Page 2

7 Silver Lake Reservoir Complex Storage Replacement Project billion gallons of treated water from the LADWP in-city storage system, placing greater reliance on the fewer remaining storage facilities, including the SLRC, to meet fluctuations in demand for drinking water and provide emergency supplies within local service areas. Both Silver Lake and Ivanhoe Reservoirs were eventually planned for removal from service as part of the replacement project involving the construction of the Headworks Reservoir, but the LADWP water supply and consumption models at the time of the Certified EIR indicated that both reservoirs were necessary to meet anticipated peak demand until the completion of the Headworks Reservoir and the new interconnecting pipeline between the River Supply Conduit and the Silver Lake Outlet Line. Although Silver Lake Reservoir was actually removed from service in 2008, ahead of the anticipated schedule, this was based on emergency circumstances related to the potential health effects of the unexpected and previously unobserved formation of bromate (a potentially toxic and carcinogenic chemical compound) in the reservoir. However, this situation was not foreseen at the time when the bypass alignment was identified in the Certified EIR as the preferred option to interconnect the River Supply Conduit and the Silver Lake Outlet Line. To resolve the concerns related to bromate formation, there was no practical solution related to Silver Lake Reservoir other than removing it from service, especially considering the relatively short-term remaining period of operation for the reservoir before it was to be permanently shut down as a treated drinking water facility. To maintain the crucial interconnection between the River Supply Conduit and the Silver Lake Outlet Line, Ivanhoe Reservoir has remained in service. However, to control the formation of bromate (which generally occurs when naturally occurring bromide contained in source water interacts with chlorine in the presence of sunlight), Ivanhoe Reservoir was covered with shade balls, which was a solution considered not appropriate for Silver Lake Reservoir, given its relatively short projected service life and that its surface area is over 10 times that of Ivanhoe Reservoir. Based on the success of expanded water conservation programs in the City of Los Angeles that were not factored into earlier demand models utilized at the time of the Certified EIR, Ivanhoe Reservoir has proven adequate on an interim basis to meet the peak demand for water from the SLRC. Since it was considered necessary at the time that Silver Lake and Ivanhoe Reservoirs remain filled and fully operational, construction of the interconnecting pipeline within the reservoirs was not deemed a feasible option. Pipeline Tunneling Concept To provide suitable access to the new pipeline for future maintenance and to minimize direct impacts to private property, the bypass alignment would necessarily need to be located within public roadways. The most direct route within roadways between the terminus of the reconstructed River Supply Conduit and the beginning of the Silver Lake Outlet Line was determined to generally follow West Silver Lake Drive. However, to maintain adequate system operating pressure based on the planning assumptions at the time, the bypass pipeline would need to be located at a depth below the surface level of the roadway that would make a conventional open-trench method of installation infeasible. Therefore, the only viable means to install the pipeline along the length of West Silver Lake Drive was by tunneling (see Figure 1). December 2013 Page 3

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9 Silver Lake Reservoir Complex Storage Replacement Project In order to minimize the number of sharp turns in the pipeline, which are more difficult to achieve with tunneling and require more frequent openings at the street surface for the pipe installation at each turning point, the bypass pipeline tunneling alignment was established as follows: From the terminus of the River Supply Conduit on West Silver Lake Drive, south along West Silver Lake Drive to a point approximately 200 feet south of Balmer Drive, parallel with a northeasterly extension of Redesdale Avenue (which does not actually intersect West Silver Lake Drive at this location); then southwesterly along Redesdale Avenue to the intersection of West Silver Lake Drive and Redesdale Avenue, about 125 feet south of Castle Street; and then southeasterly along West Silver Lake Drive to the start of the Silver Lake Outlet Line. Tunneling has the advantage of minimizing the continuous disruption at the roadway surface that characterizes a conventional open-trench method of pipeline construction. In general, it also entails the movement of a lower volume of soil, since the excavation involves boring a tunnel only as wide as the outside diameter of the pipe or tunnel lining itself rather than the larger cut required for open trench construction. However, in order to excavate the tunnel, open pits (or shafts) are required at the surface to provide access at the tunnel beginning and end points and at major turning points in the pipeline alignment. Depending on the width, depth, and number of shafts required for a tunneling project, the volume of excavated material could increase substantially. Also, these shafts generally need to remain open in the same location for extended periods during construction, whereas the surface disturbance associated with opentrench construction, while potentially more extensive, generally moves along the pathway of the pipeline as pipe segments are installed and the road is restored. However, if the open-trench construction involves a lengthy portion of a single street (as would be the case on West Silver Lake Drive for the approved bypass pipeline tunneling alignment), the disruptions to traffic on the street could be considered continuous regardless of the fact that construction would occur in a series of smaller sequential segments. The method of tunneling considered in the Certified EIR was to employ a relatively small diameter micro-tunneling machine located at the leading edge of the pipeline, which would be continually extended by pipe sections that would be fed from behind at the entry shaft and pushed forward through the tunnel by a large hydraulic jack. Excavated material (or muck) would be transported back to the entry shaft through the tunnel in haul carts, which would be lifted from the shaft and emptied at the surface, where the muck would be loaded into trucks and hauled away. In the Certified EIR, an entry shaft containing the hydraulic jacking equipment would be located on West Silver Lake Drive near Putnam Street; this shaft location is heretofore referred to as the Putnam Shaft. From the Putnam Shaft, the tunneling and pipe jacking would proceed south along West Silver Lake Drive to the point parallel with a northeasterly extension of Redesdale Avenue, where a receiving shaft would be located in West Silver Lake Drive; this shaft location is heretofore referred to as the Redesdale North Shaft. A second entry shaft would be located at the intersection of West Silver Lake Drive and Redesdale Avenue, about 125 feet south of Castle Street; this shaft is heretofore referred to as the Redesdale South Shaft. From the Redesdale South Shaft, tunneling and pipe jacking would proceed northeasterly along Redesdale Avenue to the Redesdale North Shaft, where the pipe would be joined to the pipe that had been jacked from the Putnam Shaft. From the Redesdale South Shaft to the connection with the Silver Lake Outlet Line, located about 250 feet to the southeast, the new pipeline would be constructed by means of trenching rather than tunneling because it could be installed at shallower depths in this segment and still maintain the necessary operating December 2013 Page 5

10 Introduction pressure. Similarly, from the Putnam Shaft northward to the connection with the River Supply Conduit, the pipe would be constructed by means of trenching. In addition to the installation of the bypass pipeline, the project as described in the Certified EIR includes the construction of a regulator station near the Silver Lake Recreation Center and a pressure relief station located 0.25 miles south of the SLRC. Refinement of Bypass Pipeline Tunneling Concept Based on additional engineering analysis and design development that have occurred in preparation for project construction since certification of the Silver Lake Reservoir Complex Storage Replacement Project EIR, the original tunneling concept described above has been refined. Further geotechnical investigations of subsurface soil conditions have indicated that the pipeline would need to be installed at depths beneath the surface elevation of West Silver Lake Drive ranging from 40 to 95 feet, which is deeper than originally expected. This depth of installation and the anticipated soil and groundwater conditions would require the use of a larger-diameter tunnel boring machine known as an earth pressure balance machine (EPBM), which is designed to protect the interior of the tunnel and support the tunnel face in soft ground and/or in locations where groundwater intrusion may be an issue. The EPBM would be used to cut a 10-foot diameter tunnel to accommodate a precast concrete segmental tunnel lining, within which a 66-inch diameter welded steel pipe would be installed to conduct water. The rotating cutter head of the EPBM would be pushed forward by thrust cylinders that are internal to the machine, pushing off the last completed tunnel lining ring, rather than being driven forward by pipe sections being jacked into the tunnel from the entry shaft. The segmental concrete tunnel lining would be installed within a protected shield area of the EPBM located behind the cutter head. The lining would be composed of individual segments, several of which would be required to complete the entire circumference of a lining ring. Muck would be transferred through the cutter head and out of the tunnel by means of a screw conveyor, conveyor belt, and haul carts, which would carry the muck to the entry shaft and be lifted by a crane to the surface, where the muck would be transferred to a holding area, from which it would be loaded into trucks and hauled away. After the tunnel between the shafts was completed, the welded steel pipe would be installed, with individual 20-foot long pipe sections transported into the tunnel by a self-propelled pipe carrier and welded to the preceding section of pipe. Conceptual plans for the required entry and receiving shafts and the associated construction zones at the surface of West Silver Lake Drive have been prepared based on this refinement in the tunneling approach and further design development for the interconnecting pipeline (see Figure 2 for the overall concept plan). The primary construction zones and activities are described below. Page 6

11 0 Source: LADWP 2013 I 5 0 Miles 1 Figure 2 Refined Bypass Pipeline Tunneling Alignment

12 Introduction Prior to initiating actual construction work related to the interconnecting pipeline, Ivanhoe Reservoir will be removed from service as a drinking water storage facility in late 2014, consistent with deadlines established by the California Department of Public Health related compliance with the federal Long-Term 2 Enhanced Surface Water Treatment Rule. This will be possible because the first phase of Headworks Reservoir will also be complete in late 2014, providing sufficient storage capacity to replace Ivanhoe Reservoir. The water from Headworks Reservoir will be temporarily routed through Rowena Pump Station and via an alternate distribution pathway until the completion of the new interconnecting pipeline at the SLRC (this temporary routing will be adequate on an interim basis but would not provide the required capacity, reliability, or system redundancy on a long-term basis). In order to take Ivanhoe Reservoir out of service, the shade ball cover currently on the reservoir will be removed. The reservoir will then be drained, first through normal consumption until the water level reaches the lower limit of the normal operating range, below which water will be pumped from Ivanhoe Reservoir into Silver Lake Reservoir. Once the reservoir is drained, the inlet to the reservoir will be severed and the outlet to the drinking water distribution system will be modified to prevent future cross-contamination from the non-potable water that will be stored in the reservoir. The reservoir will then be refilled, but the shade balls will not be redeployed. Ivanhoe will remain an open reservoir containing non-potable water. Redesdale North Shaft The use of the EPBM requires a shaft large enough to assemble and launch the machine and accommodate construction activities such as the transfer of the lining ring segments into the tunnel, the transfer of the muck out of the tunnel and the shaft, the transfer of the welded steel pipe segments into the tunnel, and tunnel grouting. Based on the space necessary to accommodate these activities, as well as the fact that tunneling would need to occur in two directions at the sharp turning point of the pipeline on West Silver Lake Drive (at the Redesdale North Shaft) and that a larger shaft would therefore be required in order to install the pipe elbow at this turning point, it has been determined that a single tunnel entry shaft at Redesdale North would be more appropriate in terms of limiting impacts rather than, as had been described in the Certified EIR, creating two separate entry shafts at Putnam and Redesdale South, where the size of the shafts, as well as the activities associated with launching the EPBM and tunneling, could result in complete closures of West Silver Lake Drive at these locations during extended portions of construction. Therefore, the Redesdale North Shaft would be used to launch the EPBM to tunnel both southward to the Redesdale South Shaft and northward to the Putnam Shaft. To accommodate the assembly and launch of the EPBM and the other activities associated with tunneling, the Redesdale North Shaft would be circular in shape, about 40 feet in diameter, and about 95 feet deep. Excavating and stabilizing the shaft would require the use of heavy equipment within the shaft, extensive shoring, a cast-in-place concrete floor, and a cast-in-place concrete perimeter retaining wall for the entire depth of the shaft. In order to accomplish this excavation and stabilization task, lower the EPBM components into the shaft, lower and remove the pipe carrier and other equipment, and lift the muck haul carts, a 100-ton crawler crane would be stationed adjacent to the shaft throughout construction of the shaft and tunnel. Shaft and tunnel muck would be removed by the crane and placed in a temporary walled holding area at the surface, from which it would be continually loaded by an excavator into dump trucks and hauled off site. During the construction of the shaft itself, major disruptions to traffic on West Silver Lake Drive would occur, including lengthy closures of the roadway necessitated by safety concerns related to crane operations. Page 8

13 Silver Lake Reservoir Complex Storage Replacement Project During the actual tunneling process, precast concrete tunnel lining ring segments would be continually delivered to the site on flatbed trucks, offloaded by a separate 50-ton truck-mounted crane to a staging location near the shaft, and then lowered by the crane into the shaft as required to complete the tunnel lining rings. During the installation of the welded steel pipeline within the tunnel, pipe segments would be continually delivered to the site on flatbed trucks, offloaded by the 50-ton truck-mounted crane to a staging location, and then lowered by the crane into the shaft as required. Other support functions required within the Redesdale North construction zone would include offices and tunneling apparatus control rooms, shops, parts storage buildings, water storage tanks and groundwater settlement tanks, generators, grout mixer units, tunnel ventilation equipment, and miscellaneous storage areas. To contain these various functions, the construction zone for the Redesdale North Shaft would extend from Balmer Drive on the north for approximately 600 feet southward along the west side of West Silver Lake Drive, as shown in Figure 3. The construction zone would be approximately 25 feet wide, extending eastward from the inner edge of the sidewalk located along the west side of West Silver Lake Drive. Through pedestrian access along the west side of the street would be unavailable during construction; however, sidewalk access would be maintained to the single-family residence fronting West Silver Lake Drive, just south of Balmer Drive. The location of this construction site is not only necessary to support the activities at the Redesdale North Shaft, it also has the advantage of directly fronting a minimum number of residences on West Silver Lake Drive, and it would not block any driveway access. To accommodate this construction zone and still allow for the passage of vehicular traffic along West Silver Lake Drive, the roadway would first need to be widened to the east to maintain a single travel lane in each direction. However, no parking lane, as currently exists along the west side of West Silver Lake Drive, would be available along the length of the construction zone on either side of the street. The roadway widening would require removing the existing sidewalk along the east side of the street, but room for a new sidewalk would be provided by moving the existing reservoir complex property boundary fence eastward to the top of the actual side wall of Silver Lake Reservoir. The construction zone would be fenced, and a K-rail barrier would be placed along the edge adjacent to West Silver Lake Drive. Several vehicle entrances to the construction zone from West Silver Lake Drive would be provided. Although West Silver Lake Drive adjacent to the Redesdale North construction zone would be reconfigured to continue to provide one travel lane in each direction, the tunnel entry shaft would nonetheless extend into the southbound lane due to the size and shape of the shaft. During the initial excavation of the shaft, this would require the closure of the southbound lane until a temporary bridge structure could be erected to span the shaft in the area where it intrudes into the traffic lane. This bridge would remain throughout the period of construction involving the shaft to allow for vehicle passage. However, due to potential hazards related to construction activity, sharp curves, and impeded sightlines, speed limits in the area of the Redesdale North construction zone would be reduced. December 2013 Page 9

14 NOT TO SCALE Source: LADWP 2013 I Figure 3 Redesdale North Tunneling Shaft

15 Silver Lake Reservoir Complex Storage Replacement Project In addition, during construction, the boom from both the 100-ton crawler crane and the 50-ton truck-mounted crane would need to swing out over the traffic lanes to perform some operations because the steep slope located along the west edge of the construction zone would limit the range of the booms movement. As discussed above, for the 100-ton crawler crane, these operations would include supporting the excavation and stabilization of the shaft, lowering and removing the EPBM components and other equipment into the shaft, and lifting the muck haul carts from the shaft. For the 50-ton truck-mounted crane, these operations would involve offloading tunnel lining ring segments and pipe sections from trucks and lowering them into the shaft as needed. When these activities were actually occurring, traffic in both directions on West Silver Lake Drive adjacent to the construction zone, as well as pedestrian traffic on the sidewalk on the east side of the road, would need to be temporarily halted because of the potential safety hazard to motorists and pedestrians. As discussed above, the Redesdale North Shaft would be used to launch the EPBM and excavate both the tunnel southward to the Redesdale South Shaft and the tunnel northward to the Putnam Shaft. The activities involving the cranes at the Redesdale North Shaft, including the site preparation and shaft construction, would take place continually over approximately a 2.5-year period, throughout which frequent and potentially lengthy disruptions to traffic on West Silver Lake Drive would occur during construction hours, which, as discussed in the Certified EIR, may take place Mondays through Saturdays. Redesdale South Shaft Because it would not be used to launch the EPBM, remove material related to tunnel excavation, or install the tunnel lining, the Redesdale South Shaft would not need to support the same type and level of construction activity as the Redesdale North Shaft. It would serve as a receiving shaft for the EPBM that would have originated at the Redesdale North Shaft. The EPBM would be lifted from the shaft by a 100-ton crawler crane, disassembled, and transported back to the Redesdale North Shaft to initiate the tunneling to the Putnam Shaft. Since all materials related to the actual tunneling between the Redesdale North Shaft and the Redesdale South Shaft would originate at the north shaft, no delivery of tunneling materials would occur at the south shaft. However, since tunneling activities from the Redesdale North Shaft to the Putnam Shaft would be initiated immediately after the completion of the tunnel to the Redesdale South Shaft, space would be limited in the north shaft. Therefore, the actual welded steel pipe between the Redesdale North and South Shafts would probably be installed from the south shaft concurrently with the tunneling between Redesdale North and Putman. In this manner, the overall length of construction could be minimized compared to conducting all tunneling and pipe installation activities sequentially from only North Redesdale. The pipeline would also make a sharp turn to the southeast at the Redesdale South Shaft and rise in elevation to continue on to the connection with the Silver Lake Outlet Line. To accommodate these various activities and spatial requirements, the shaft would be circular in shape, about 30 feet in diameter, and about 40 feet deep. As at the Redesdale North Shaft, excavating and stabilizing the shaft would require the use of heavy equipment within the shaft, extensive shoring, a cast-in-place concrete floor, and a cast-in-place concrete perimeter retaining wall for the entire depth of the shaft. A 50-ton truck-mounted crane would be used to support the excavation and stabilization of the shaft, lower and remove the pipe carrier and other equipment, and lower pipe segments into the shaft. Shaft muck would be placed in a temporary walled holding area at the surface, from which it would be loaded by an excavator into dump trucks and hauled off site. During the construction of the shaft itself, major disruptions to traffic on West Silver Lake Drive would occur, including lengthy closures of the roadway necessitated by safety concerns related to crane operations. December 2013 Page 11

16 Introduction During the installation of the welded steel pipeline within the tunnel, pipe segments would be continually delivered to the site on flatbed trucks, offloaded by the crane, and lowered into the shaft, with individual pipe sections transported into the tunnel by the self-propelled pipe carrier and welded to the preceding section of pipe. The Redesdale South construction zone would also support the pipeline installation from the shaft, located at the northeast corner of West Silver Lake Drive and Redesdale Avenue, to the beginning of the Silver Lake Outlet Line, located about 250 feet to the southeast. As discussed above, this segment of the pipeline would be constructed by means of an open trench because it could be installed at shallower depths compared to the tunneling segments. To contain these functions, the Redesdale South construction zone would extend approximately 275 feet along West Silver Lake Drive to the east of Redesdale Avenue, as shown in Figure 4. The construction zone would be about 30 feet wide and, to avoid damage to existing mature trees located in the Silver Lake Recreation Center property, would extend southward from the curb along the north side of West Silver Lake Drive. The construction zone would be fenced, and a K-rail barrier would be placed along the edge adjacent to West Silver Lake Drive. The street would be narrowed to a single traffic lane adjacent to the Redesdale South construction zone, which would generally require a detour for either eastbound or westbound traffic throughout construction, which is expected to last nearly 3 years, including the open-trench pipeline installation connecting to the Silver Lake Outlet Line and supporting the construction of a regulator station (see below). In addition, similar to the conditions at the Redesdale North Shaft, the boom from the cranes must swing out over the traffic lanes to perform operations because the mature trees located immediately north of the shaft would limit the range of the boom s movement. As discussed above, these operations would include supporting the excavation and stabilization of the shaft, retrieving the EPBM from the shaft, and offloading pipe sections from trucks and lowering them into the shaft. When these activities were actually occurring, traffic on West Silver Lake Drive adjacent to the construction zone would need to be temporarily halted because of the potential safety hazard to motorists. After completion of the pipeline installation (including both the tunneling and open trench activities), the Redesdale South construction zone would continue to be used to support the construction of the regulator station, which is necessary to control water pressure at the Silver Lake Outlet Line. The regulator station and associated pipelines would occupy a footprint of approximately 30 feet by 45 feet in the lawn of the Silver Lake Recreation Center, north of the bypass line near its connection to the Silver Lake Outlet Line. In relation to the bypass pipeline alignment, no other location for the regulator station would be feasible because of the depth of the pipeline in the tunnel as it passes adjacent to other open areas of the SLRC bordering West Silver Lake Drive. The station would be buried below grade, and construction would require relatively substantial excavation work and concrete deliveries. The construction of the regulator station, as described in the Certified EIR, would take approximately 6 to 9 months to complete. Page 12

17 NOT TO SCALE Source: LADWP 2013 I Figure 4 Redesdale South Tunneling Shaft

18 Introduction Putnam Shaft The Putnam Shaft would function as a receiving shaft for the EPBM that would have originated at the Redesdale North Shaft. The EPBM would be lifted from the shaft by a 100-ton crawler crane, disassembled, and transported off site since the project tunneling activity would be complete. Since all materials related to the tunneling between the Redesdale North Shaft and the Putnam Shaft would originate at the Redesdale North Shaft, no delivery of tunneling materials would occur at the Putnam Shaft. In addition, the welded steel pipe between the Redesdale North and Putnam Shafts would be installed from the Redesdale North Shaft, where individual pipe sections would be transported into the tunnel by the self-propelled pipe carrier and welded to the preceding section of pipe. The pipeline would rise in elevation at the Putnam Shaft to continue on to the connection with the River Supply Conduit in Armstrong Avenue. Because the Putnam Shaft supports no tunneling activities (other than the retrieval of the EPBM) and relatively minor pipeline installation activities, it would be smaller than either the Redesdale North or Redesdale South Shafts, and it would be rectangular in shape at about 20 feet by 30 feet, running longitudinally in the direction of the pipeline and the roadway. However, the Putnam Shaft would be 70 feet deep, and, as at the Redesdale North and Redesdale South Shafts, excavation and stabilization of the shaft would require the use of heavy equipment within the shaft, extensive shoring, a cast-in-place concrete floor, and a cast-in-place concrete perimeter retaining wall for the entire depth of the shaft. A 50-ton truck-mounted crane would be used to support the excavation and stabilization of the shaft and lower pipe segments and required equipment into the shaft. Shaft muck would be placed in a temporary walled holding area at the surface, from which it would be loaded by an excavator into dump trucks and hauled off site. During the construction of the shaft itself, major disruptions to traffic on West Silver Lake Drive would occur, including lengthy closures of the roadway necessitated by safety concerns related to crane operations. To contain these functions, the Putnam Shaft construction zone would extend from Armstrong Avenue on the north approximately 350 feet southward along the east side of West Silver Lake Drive, as shown in Figure 5. The site would be about 25 feet wide, extending westward from the curb on the east side of the street. This would leave enough road width to maintain a single travel lane in each direction, but no parking lanes, as currently exist on both sides of West Silver Lake Drive, would be available along the length of the construction zone. In addition, three to four private driveways would be blocked for certain periods during construction. The construction zone would be fenced, and a K-rail barrier would be placed along the edge adjacent to West Silver Lake Drive. Construction activities at the Putnam Shaft area would last approximately 2 years, including connecting to the River Supply Conduit in Armstrong Avenue. Similar to the conditions at the Redesdale North and Redesdale South Shafts, the boom from the cranes must swing out over the traffic lanes to perform operations to avoid swinging over residential properties located to the east of the construction zone. As discussed above, these operations would include supporting the excavation and stabilization of the shaft, retrieving the EPBM from the shaft, and offloading pipe sections from trucks and lowering them into the shaft. While these activities would be of a shorter total duration at the Putnam Shaft than at the Redesdale North or South Shafts, when they were actually occurring, traffic in both directions on West Silver Lake Drive adjacent to the construction zone would need to be temporarily halted because of the potential safety hazard to motorists. Page 14

19 NOT TO SCALE Source: LADWP 2013 I Figure 5 Putnam Tunneling Shaft

20 Introduction In addition to the construction activities related to the tunneling shaft itself, the Putnam construction zone would also support the pipeline installation from the shaft northward approximately 225 feet to the connection to the River Supply Conduit. As discussed above, this segment of the pipeline would be constructed by means of an open trench because compared to the tunneling segments it would be installed at a shallower depth of about 30 feet. Because of the depth of excavation required and the necessary shoring activities, this open trench installation would take up to 6 months, occurring after the completion of tunneling activities at the site. Due to the location of the River Supply Conduit along the northern side of Armstrong Avenue and the depth of the excavation, the roadway may be narrowed to a single lane of through traffic for several months during the hours of construction. However, it is anticipated that the open trench would be covered with steel plates to allow for the passage of traffic during hours when construction would not be occurring. Shaft Closures After completion of the pipeline installation from the Redesdale North Shaft to the Putnam Shaft, the pipe segments connecting the two tunnel reaches (i.e., Redesdale North to Redesdale South and Redesdale North to Putnam) would be installed at the Redesdale North Shaft. After this connection is made, all equipment would be removed from the shaft, the upper 8 feet of the perimeter concrete retaining wall would be removed, and the shaft would be backfilled with soilcement slurry to completely fill voids and provide an essentially non-compressive mass. The construction zone facilities, equipment, and barriers would be removed, the pavement restored, and West Silver Lake Drive and the adjacent sidewalks returned to their original alignments. After completion of the connection to the River Supply Conduit, the upper 8 feet of the perimeter retaining wall at the Putnam Shaft would be removed, and the shaft would be backfilled with soil-cement slurry. The construction zone equipment and barriers would be removed and the pavement restored. After completion of the connection to the Silver Lake Outlet Line, the upper 8 feet of the perimeter retaining wall at the Redesdale South Shaft would be removed, and the shaft would be backfilled with soil-cement slurry. However, portions of the South Redesdale Shaft construction zone would continue to support the construction of the regulator station located in the lawn of the Silver Lake Recreation Center (see Figure 4). After completion of the regulator station, the construction zone equipment and barriers would be removed and the pavement restored. Pressure Relief Station In addition to the above facilities, which would be located generally adjacent to the SLRC, a relief station, as described in the Certified EIR, would be constructed south of the SLRC to release water in the case of excess buildup of pressure in the Silver Lake Outlet Line. This station would be necessary because the open-air reservoirs in the SLRC, which would be entirely bypassed by the new pipeline, would no longer function, as they currently do, to relieve excess pressure that may occur in the distribution system. The station would be located at the intersection of West Silver Lake Drive and Silver Lake Boulevard, approximately 0.25 miles south of the SLRC, where water could be diverted into an existing storm drain if required during an excess pressure event. The station would include a vault buried in Silver Lake Boulevard and the installation of approximately 100 feet of 12-inch diameter pipe, which would be constructed by open-trench method, crossing Silver Lake Boulevard. Construction of the relief station would take approximately 2 months, which would occur concurrently with construction of the bypass pipeline. Page 16

21 Silver Lake Reservoir Complex Storage Replacement Project Construction Activities and Sequencing The bypass pipeline tunneling alignment, including the construction of the regulator station at the Silver Lake Recreation Center and the pressure relief station south of the SLRC, would take a total of approximately 3 years to complete. The basic nature and sequence of activities, some of which would overlap in time, would include: Construction of the Redesdale North, Redesdale South, and Putnam Shafts and construction zones Tunneling with the EPBM, including the installation of the precast tunnel lining, from the Redesdale North Shaft to the Redesdale South Shaft Retrieval of the EPBM at the Redesdale South Shaft and return of the EPBM to the Redesdale North Shaft Installation of the welded steel pipe from the Redesdale South Shaft to the Redesdale North Shaft Tunneling with the EPBM, including the installation of the precast tunnel lining, from the Redesdale North Shaft to the Putnam Shaft Installation of the welded steel pipe from the Redesdale North Shaft to the Putnam Shaft Open-trench installation of the pipe from the Putnam Shaft to the terminus of the River Supply Conduit in Armstrong Avenue, including the connection of the lines Open-trench installation of the pipe from the Redesdale South Shaft to the beginning of the Silver Lake Outlet Line, including the connection of the lines Construction of the pressure regulator station near the Silver Lake Recreation Center Construction of the pressure relief station at the intersection of West Silver Lake Drive and Silver Lake Boulevard Table 1 below indicates the basic construction activities, in approximate sequential order, for the bypass pipeline tunneling alignment, including a preliminary estimate of the start month and the duration of the activities. December 2013 Page 17

22 Introduction Table 1 Bypass Pipeline Tunneling Alignment Construction Activities ACTIVITY START MONTH DURATION (months) Mobilization, including equipment mobilization, materials acquisition, and project staging areas Redesdale North Shaft site preparation, including: West Silver Lake Drive widening Construction zone fencing and barriers Support facilities construction Shaft overburden and rock excavation Shaft cast-in-place floor slab and retaining wall Tunneling plant and EPBM assembly Redesdale South Shaft site preparation, including: Construction zone fencing and barriers Support facilities construction Shaft overburden and rock excavation Shaft cast-in-place floor slab and retaining wall Putman Shaft site preparation, including: Construction zone fencing and barriers Support facilities construction Shaft overburden and rock excavation Shaft cast-in-place floor slab and retaining wall Redesdale North to Redesdale South tunnel excavation 12 2 Retrieval of EPBM from Redesdale South; disassembly of EPBM; transport of EPBM to Redesdale North; reassembly of EPBM 14 2 Redesdale South to Redesdale North pipeline installation 14 2 Redesdale North to Putnam tunnel excavation 16 5 Redesdale South shaft piping installation; shaft closure 16 4 Retrieval of EPBM at Putnam; disassembly of EPBM; transport of EPBM off site 21 1 Redesdale North to Putnam pipeline installation 21 5 Redesdale South open trench installation pipeline to Silver Lake Outlet Line Redesdale North Shaft plant removal; shaft piping installation; shaft closure; site restoration Putnam shaft piping installation; connection to River Supply Conduit; shaft closure; site restoration Regulator Station at Silver Lake Recreation Center; site restoration 28 8 Pressure Relief Station at West Silver Lake Drive and Silver Lake Boulevard 34 2 Demobilization 36 1 Page 18

23 Silver Lake Reservoir Complex Storage Replacement Project Construction Quantities The bypass line tunnel construction described above would entail the excavation of a tunnel approximately 4,900 feet in length, including about 1,200 feet between the Redesdale North Shaft and the Redesdale South Shaft, and 3,700 feet between the Redesdale North Shaft and the Putnam Shaft. The tunnel would include a 10-foot diameter precast concrete lining, within which a 66-inch diameter welded steel pipe would be installed. The bypass pipeline tunneling alignment would also involve about 250 feet of conventional open-trench pipe installation between the Redesdale South Shaft and the start of the Silver Lake Outlet Line and about 225 feet of open-trench pipe installation between the Putnam Shaft and the terminus of the River Supply Conduit at Armstrong Avenue. Additionally, about 100 feet of open trench pipe installation would occur from West Silver Lake Drive across Silver Lake Boulevard for the pressure relief station. This work would generate a total of about 41,450 cubic yards of excavated material, all of which would be hauled by trucks to an off-site disposal facility. About 26,000 cubic yards of concrete or slurry, which would be delivered by truck, would be required for structures (e.g., retaining walls), thrust block encasements, slurry backfills, and other purposes. About 15,200 one-way truck trips would be required throughout construction to deliver and remove construction equipment and support facilities, deliver material and components, deliver concrete and slurry, and haul away excavated material, with each inbound and each outbound trip counted as a one-way trip. The number of truck trips per day would vary substantially during the project, depending on the type, number, and duration of activities occurring in a given period. Based on a preliminary breakdown of the construction schedule and tasks, the number of daily peak truck trips would range between about 75 and 80 for about a 1-month period. The lengthiest peak period involving relatively substantial truck traffic would be during the tunneling between the North Redesdale Shaft and the Putman Shaft, when an average of about 45 daily truck trips would occur over a consecutive 5-month period. The number of pieces of operating equipment (i.e., cranes, excavators, generators, etc., but excluding trucks, which are accounted for separately under truck trips) would also vary during construction, depending on the type, number, and duration of activities occurring in a given period. Based on a preliminary breakdown of the construction schedule and tasks, the daily peak number of on-site operating equipment would be about 40 for a 1-month period during the simultaneous excavation of the tunnel between the North Redesdale Shaft and the South Redesdale Shaft and the excavation of the Putnam Shaft. Outside of this peak period, the number of pieces of on-site equipment would be fewer than 30 per day. The number of construction personnel on site would likewise vary during construction, depending on the type, number, and duration of activities occurring in a given period. Based on a preliminary breakdown of the construction schedule and tasks, the daily peak number of personnel would be for about a 1-month period during the simultaneous excavation of the tunnel between the North Redesdale Shaft and the South Redesdale Shaft and the excavation of the Putnam Shaft, when an average of about 35 personnel would be on site each day. Outside of this peak period, the number of on-site personnel would be 30 or fewer per day. December 2013 Page 19

24 Introduction 1.4 Reconsideration of In-Reservoir Pipeline Alignment Background Based on the magnitude of the construction effort described above related to tunneling for the bypass pipeline, a number of factors have contributed to a reconsideration of the potential to route the interconnecting pipeline between the River Supply Conduit and the Silver Lake Outlet Line through, rather than around, the SLRC. The most important of these factors is that since the approval of the bypass pipeline tunneling alignment in 2006, Silver Lake Reservoir has been removed from service as a drinking water storage facility to prevent the formation of bromate in the water supply. Although Silver Lake Reservoir remains filled with non-potable water, it no longer provides a physical link between the River Supply Conduit and the Silver Lake Outlet Line, as it did when the bypass pipeline was originally proposed and studied in the Certified EIR. This physical link is currently provided solely via Ivanhoe Reservoir, which is supplied by the River Supply Conduit and connected to the Silver Lake Outlet Line via a separate pipeline. Although the loss of Silver Lake Reservoir has reduced local storage capacity that had been utilized to meet daily fluctuations in demand and provide water during emergency shortages, based on expanded water conservation programs, Ivanhoe Reservoir (which has been covered with shade balls to curtail the formation of bromate) provides the capability to respond to most circumstances on an interim basis during construction of the Headworks Reservoir, which will permanently replace the storage function of the SLRC. The physical isolation of Silver Lake Reservoir from the drinking water system and the resultant lack of dependence on the reservoir for drinking water supply and distribution have now created a situation under which the reservoir could be drained to allow for construction of the pipeline within the reservoir without compromising the operational integrity of the system. The assumptions regarding the minimum acceptable operating pressure for the interconnecting pipeline have also changed since the Certified EIR was prepared. In addition to being a critical factor relative to the delivery of water through the transmission system, the operating pressure of a pipeline also functions as a force against the intrusion of contaminants that could potentially penetrate the pipeline through small openings. During early project planning stages, a pressure of 10 pounds per square inch (psi) reflected a highly conservative assumption in relation to California Department of Public Health requirements for the protection of drinking water mainlines from the intrusion of contaminants. This assumption regarding minimum pressure was a primary factor in the selection of the tunneling (rather than trenching) approach to the pipeline construction because of the depth of installation to achieve the minimum pressure. However, California Department of Public Health requirements can actually be met at pressures as low as 5 psi. A 5 psi pressure requirement allows for a depth of installation that would make trenching (rather than tunneling) feasible within certain limits of the proposed bypass line alignment. South of Hawick Street, adjacent to the northwest corner of Silver Lake Reservoir, the depth of installation required to maintain 5 psi could not be feasibly achieved by means of trenching, and tunneling would be required. However, north of Hawick Street, trenching would represent a feasible means for pipeline installation while still maintaining minimum operational pressure in the line. In addition, the required minimum pressure could also be achieved with relatively minimal trenching within Silver Lake Reservoir itself because of the lower elevation of the reservoir floor. While cross-contamination of the water supply associated with placing the pipeline within a reservoir containing non-potable water is a potential concern, several characteristics of the proposed pipeline would essentially eliminate the potential for cross-contamination. The use of welded steel pipe with welded joints, as is proposed for the project, would largely eliminate Page 20

25 Silver Lake Reservoir Complex Storage Replacement Project potential seepage points. The steel pipe used throughout the project would also have a cement mortar outer coating and inner lining that would strengthen the pipe and provide an additional barrier of separation. Furthermore, the sections of pipeline that would be located within the reservoir would also be nested within an outer welded steel pipe sleeve that would in turn be encased in concrete. The use of these multiple barriers of separation would prevent crosscontamination of drinking water contained within a pipeline located in a reservoir containing nonpotable water, even under circumstances when water pressure in the line was temporarily reduced below normal minimum values. While the removal of Silver Lake Reservoir from service and a reevaluation of the operating pressure requirements for the interconnecting pipeline have provided an opportunity, from an operational perspective, to reconsider an alternative alignment that routes the pipeline through the SLRC, recent developments related to pipeline construction in the Silver Lake community have also prompted this reconsideration. The construction of the Lower Reach River Supply Conduit Unit 4 (which is the southernmost link of the trunk line that will transport water from the Headworks Reservoir in Griffith Park to the vicinity of the SLRC) created substantial controversy in the Silver Lake community related to traffic disruption, pedestrian safety, air pollution, noise, and temporary loss of access to property. In light of the concerns associated with the construction of the River Supply Conduit and the magnitude of the construction effort for the bypass pipeline tunneling alignment (together with the changes to the operational conditions that had previously influenced the selection of the tunneling approach), LADWP has endeavored to explore an alternative means to achieve the required pipeline interconnection between the River Supply Conduit and the Silver Lake Outlet Line. Therefore, the intent of an alternative alignment would be to minimize, to the extent possible, construction activity within public roadways; the quantity of earthwork, equipment, and truck trips; and the duration of construction. An alignment that would route the pipeline within Silver Lake Reservoir would achieve these objectives by minimizing in-street construction and reducing the magnitude and duration of construction. Some construction within public roadways would still be required to extend a pipeline from the terminus of the River Supply Conduit in Armstrong Avenue to the SLRC, but routing the line through Silver Lake Reservoir would help minimize the extent of construction activities in public roadways and the general magnitude of the construction effort. In order to reach Silver Lake Reservoir from the River Supply Conduit, the pipeline would still need to be routed within West Silver Lake Drive between Armstrong Avenue and the northwest corner of the reservoir, where the line could turn eastward, away from the road and into the reservoir, as shown in Figure 6. Even though some in-street construction would still be required, the in-reservoir pipeline alignment would nonetheless help minimize the extent and magnitude of disruption to local roadways when compared to an alignment that entirely bypasses the reservoir by means of tunneling. This approach would also generally help reduce the total volume of excavation, the number of truck trips, and the overall duration of construction. The in-reservoir pipeline alignment alternative would require temporarily draining Silver Lake Reservoir during construction. However, based on outreach by LADWP, public opinion in the surrounding community is generally supportive of temporarily draining the reservoir as a means of limiting the magnitude and duration of construction and the extent of disruption on local roadways. December 2013 Page 21

26 Source: LADWP 2013 I Figure 6 In-Reservoir Pipeline Alignment

27 Silver Lake Reservoir Complex Storage Replacement Project In-Reservoir Pipeline Alignment Open-trench pipeline construction does not require launching or receiving shafts or the longterm use of stationary construction zones necessary to support the various activities associated with tunneling. An open-trench installation is instead characterized by construction activities at the surface that move forward along the pathway of the pipeline as sections of pipe are installed. The general process for open-trench construction in a roadway involves a number of sequential steps. First, the roadway adjacent to the defined construction zone would be reconfigured and/or restriped, as appropriate, to allow for continued safe passage of vehicles during construction. The construction zone would then be segregated from the roadway and sidewalk with fencing and, adjacent to the traffic lanes, with a K-rail barrier. I-beam piles, which would be used to support the shoring system required to stabilize the trench side walls, would be placed in predrilled holes located along the perimeter of the area to be trenched, and the pavement would be saw cut along the perimeter to provide a clean edge. The road pavement within the trench area would then be demolished with an excavator, and the debris would be loaded into dump trucks to be hauled off site. The trench would then be excavated, which would include the installation of a vertical shoring system to provide stability as the trench is progressively deepened. The excavated material would be loaded into dump trucks and hauled off site. Once a trench of sufficient length has been excavated, welded steel pipe sections would be delivered to the site on a flatbed truck and offloaded to be placed in the trench. A 40-foot long section of welded steel pipe would be lowered into the trench and welded to the preceding pipe section. When several sections of pipe have been installed, the shoring structures supporting the trench adjacent to the pipe would be removed and the trench would be backfilled with soilcement slurry to quickly and completely fill voids and provide an essentially non-compressive mass in the trench. This would occur at the same time that trenching and pipe installation work would continue in the forward areas of the trench. A temporary bulkhead structure would be placed across the trench to contain the slurry so that it does not interfere with continued construction in the forward portions of the trench. The entire process of installing three to four sections of pipe, including backfilling of the trench, would take approximately 10 to 15 work days to complete. This method of continually backfilling the trench once a portion of the pipeline is complete helps limit the size of the active construction area and the extent of open trench at a given time. After completion of the pipeline installation in the defined construction zone, including the removal of the shoring structures and the backfilling of the trench, the fence and the traffic barriers would be removed, and the roadway within the construction zone would be repaved and restriped as necessary. Based on this construction process, the required depth of installation for the interconnecting pipeline, and an analysis of the site conditions on West Silver Lake Drive, preliminary plans for the trenching operations and the supporting construction zones have been developed. The construction for the in-reservoir pipeline alignment would be subdivided into three primary work areas, as shown in Figures 7 and 8. Work Area 1 would extend along the east side of West Silver Lake Drive from Armstrong Avenue on the north to approximately Tesla Avenue on the south. Work Area 2 would extend along the east side of West Silver Lake Drive from Tesla Avenue on the north to approximately 300 feet north of Hawick Street, adjacent to the northwest corner of Silver Lake Reservoir. Work Area 3 would encompass an area contained essentially within the SLRC and primarily within Silver Lake Reservoir itself, extending southward along the west side of the reservoir and terminating just north of the reservoir dam. As currently planned, the work within these areas would proceed as described below. While the exact sequencing of December 2013 Page 23

28 Introduction the work between the different zones may change, the general type and extent of work and the construction processes required in each zone would remain basically as described. Prior to initiating actual construction work related to the interconnecting pipeline, Ivanhoe Reservoir will be removed from service as a drinking water storage facility in late 2014, as described above under the bypass pipeline tunneling alignment. After removal from service, it will remain an open reservoir containing non-potable water. Silver Lake Reservoir would then be drained to facilitate construction of the pipeline. The water in Silver Lake Reservoir would be pumped into Ivanhoe Reservoir to refill Ivanhoe Reservoir following removal of the shade balls and the severing and/or modifications of the reservoir inlet and outlet. Water that would not be pumped into Ivanhoe Reservoir would be drained, depending on water quality, into the storm system or sewer system. It would take approximately 3 months for the reservoir to be completely drained and dried out prior to the start of construction. Work Area 1 Once the reservoir was drained and dried out, work is anticipated to begin simultaneously in Work Areas 1 and 3. Work Area 1 would be approximately 28 feet wide, extending westward from the face of the curb located along the east side of West Silver Lake Drive. This would leave enough road width to maintain a single vehicle travel lane in each direction. However, no parking lanes, as currently exist on both sides of West Silver Lake Drive, would be available along the length of the construction zone. Work Area 1 would front eight residential driveways on the east side of the street, but vehicular access to the driveways would generally be maintained throughout construction since a limited segment of trench would be open at a given time. Even in instances where an open trench fronted a driveway, access would normally be maintained with steel plates spanning the trench. From an existing vault located in West Silver Lake Drive near Armstrong Avenue, an approximately 8.5-foot wide trench would be excavated and shored to install pipe connecting to the River Supply Conduit, which is located along the northern side of Armstrong Avenue. This trench would be approximately 30-feet deep and 100-feet long. Because of the depth of excavation required and the necessary shoring activities, this open trench installation would take up to 6 months. This installation north of the vault would be similar to that which would occur under the bypass pipeline tunneling alignment discussed above. Southward of the vault, an approximately 8.5-foot wide trench would also be excavated and shored. The trench would need to be up to about 30 feet deep where the new pipeline would connect to the existing vault structure. However, the elevation of the pipe would rise within a short distance of this connection, and the trench within the remainder of Work Area 1 would generally be less than 15 feet deep. The trenching and pipe installation work south of the vault would occur concurrently with the work north of the vault to minimize the total length of construction in Work Area 1. As the trench was excavated, the material would be loaded into dump trucks parked adjacent to the trench within the fenced construction zone and hauled via West Silver Lake Drive into Silver Lake Reservoir (which would have been drained), where it would be spread on the bottom of the reservoir. After all the pipe had been installed and the trench backfilled in Work Area 1, the construction zone barriers would be removed, and the pavement would be restored. The total duration of construction in Work Area 1 is anticipated to last approximately 6 months, including the repaving of the roadway. Page 24

29 I Source: LADWP 2013 Figure 7 Work Areas 1 and 2

30 I Source: LADWP 2013 Figure 8 Work Area 3